Organic phosphonic acid compound corrosion protection in aqueous systems

ABSTRACT

The invention disclosed relates to organo-phosphonic acid compounds in combination with azole compounds and zinc salts for use to inhibit metal corrosion in aqueous systems. The organophosphonic acid compounds include alkylene polyphosphonic acids, and the water-soluble salts and esters thereof.

United States Patent [191 Hwa [451 Apr. 9, 1974 1 ORGANIC PHOSPHONIC ACID COMPOUND CORROSION PROTECTION IN AQUEOUS SYSTEMS [75] Inventor: Chih Ming Hwa, Palatine, Ill.

[73] Assignee: W. R. Grace & Co., New York,

122] Filed: Oct. 26, 1972 I21 1 Appl. No.: 300,936

Related US. Application Data [63] Continuation of Ser. No. 645,600, June 13, 1967,

abandoned, which is a continuation-in-part of Ser. No. 581,151, Sept. 22, 1966. Pat. No. 3,431,217.

[5 6] References Cited UNITED STATES PATENTS 3,483,133 12/1969 Hatch et a1. 252/389 A 3,532,639 10/1970 Hatch et a1. 252/389 A Primary ExaminerCarl D. Quarforth Assistant Examiner-Irwin Gluck Attorney, Agent, or Firm-Eugene M. Bond 57] ABSTRACT The invention disclosed relates to organo-phosphonic acid compounds in combination with azole compounds and zinc salts for use to inhibit metal corrosion in aqueous systems. The organo-phosphonic acid compounds include alkylene polyphosphonic acids, and the water-soluble salts and esters thereof.

4 Claims, No Drawings ORGANIC PHOSPHONIC ACID COMPOUND CORROSION PROTECTION IN AQUEOUS SYSTEMS This application for United States Letters patent is a continuation of US. Pat. application Ser. No. 645,600 and now abandoned, filed June 13, 1967, which in turn is a continuation-in-part of US. Pat. application Ser. No. 58l,l5l, filed Sept. 22, 1966, and now US. Pat. No. 3,431,217.

This invention relates to a method and composition for preventing corrosion of metal surfaces in contact with aqueous systems.

in summary the corrosion inhibiting composition of this invention consists essentially of from 1 to 80 weight percent of an alkylene polyphosphonic acid having one of the following formulae A, B or C:

wherein m is an integer from 1 to 10, R is hydrogen, or an alkyl group having from 1 to 4 carbons and R is hydroxyl, hydrogen, or an alkyl group having from 1 to 4 carbons, R is an alkyl group having 1 to carbons, benzyl or phenyl, R is an aliphatic radical having from 1 to 10 carbons, and the water-soluble salts and esters thereof; or mixtures thereof, and from 1 to 80 weight percent of an azole compound selected from a group consisting of triazoles, pyrazoles, imidazoles, isoxazoles, oxazoles, isothiazoles, thiazoles and mixtures thereof, and/or from 1 to 95 weight percent of a watersoluble zinc salt. Aqueous solutions of l to 70 weight percent of this composition are also encompassed within this invention.

in summary, the method of this invention for preventing corrosion of metals in contact with an aqueous liquid comprises maintaining in the aqueous liquid from 1 to 10,000 ppm. of the alkylene polyphosphonic acid, salts or esters thereof, and from 1 to 10,000 ppm. of the azole compound and/or from 1 to 10,000 ppm. of a water-soluble zinc salt.

Water-soluble inorganic chromates are widely used to treat industrial water systems to prevent corrosion of metal parts in contact therewith. When these chromates are employed alone, they are used in concentrations as low as 200 ppm. and as high as 10,000 ppm., depending upon the protection needed and the permissible cost. When these chromates are used in combinations with molecularly dehydrated inorganic phosphates such as disclosed in US Pat. No. 2,711,391,

chromate concentrations as low as 20 ppm. have been found adequate in mild corrosive systems. Therefore, combinations of chromates and molecularly dehydrated phosphates are widely used.

Although chromates are highly effective corrosion inhibitors, their use is subject to several difficulties. Chromates cause serious skin and eye irritations, and chromates cannot be used in aqueous systems such as cooling towers or air-wash units where the resulting spray will contact people. Chromate solutions, because they are toxic, often require chemical treatment before being discharged to waste systems. Furthermore, chromates degrade organic compounds mixed therewith, limiting the types or organic compounds which can be mixed with the chromates in dry mixtures and aqueous solutions.

The use of molecularly dehydrated inorganic phosphates in aqueous systems causes serious problems because the polyphosphates hydrolyze to form alkaline earth metal orthophosphates, causing scaling and fouling of the aqueous systems treated. Because of this hydrolysis, excess quantities of the polyphosphates must be employed.

It is an object of this invention to provide a nontoxic composition for treating aqueous systems to prevent corrosion of metal surfaces in contact therewith which does not introduce orthosphophates to the aqueous systems. The composition contains an organic phosphonic acid compound in combination with an azole compound and/or a watersoluble zinc salt.

The compositions of this invention are useful for treating a variety of aqueous systems, that is, any aqueous system corrosive to metal surfaces in contact therewith. Suitable systems which can be treated according to this invention include water treatment systems, cooling towers, water circulating systems, and the like wherein fresh water, brines, sea water, sewage effluents, industrial waste waters, and the like are circulated in contact with metal surfaces. These compounds are useful in acid pickling baths, radiator coolers, hydraulic liquids, antifreezes, heat transfer mediums, and petroleum well treatments. The process of this invention is suitable for reducing the corrosion of iron, copper, aluminum, zinc and alloys containing these metals such as steel and other ferrous alloys, brass, and the like which are in contact with corrosive aqueous systems.

All concentrations are given herein as weight percents unless otherwise specified.

The compositions of this invention contain from 1 to percent of an organo-phosphonic acid compound. The preferred organo-phosphonic acid compound for use in the composition of this invention is an alkylene diphosphonic acid having the foregoing Formula A, such as those disclosed in US. Pat. Nos. 3,214,454 and 3,297,578, the entire disclosures of which are incorporated herein by reference. Also suitable is an alkylene diphosphonic acid having the foregoing Formula B or Formula C such as those disclosed in U.S. Pat. No.

3,303,139, the entire disclosure of which is incorporated herein by reference. Suitable acids of this type include methylenediphosphonic acid; ethylidenediphosdihydroxyl, 1,4-diethyl, tetramethylenediphosphonic acid; 1,3-dihydroxy 1,3-dipropyl, trimethylenediphosphonic acid; 1,4-dibutyl, tetramethylenediphosphonic acid; dihydroxy, diethyl, ethylenediphosphonic acid; 4-hydroxy, 6-ethyl, hexamethylenediphosphonic acid; l-hydroxy, butylidenediphosphonic acid; butylidenediphosphonic acid; l-aminoethanel ,l-diphosphonic acid; l-aminopropanel, l-diphosphonic acid; 1- aminobenzyll ,l-diphosphonic acid; 1,6- diaminohexane-1,l,6,6-tetraphosphonic acid; I- aminoethane-l,l-diphosphonic acid monethyl ester. and l-amino-2-phenylethane1,1-diphosphonic acid. The water-soluble salts of these acids such as the alkali metal, alkaline earth metal, zinc, cobalt, chromium, lead, tin, nickel, ammonium, or amine and lower alkanol amine salts can be used. Also, esters of these acids with an aliphatic alcohol having from 1 to 4 carbons, or mixtures of the above acids, salts or esters can be used. Use of mixtures of any of the general types of organo-phosphonic acid compounds described above is also contemplated within the scope of this invention.

It will be seen from the foregoing listing of acid compounds within the scope of Formula A and a number of the examples which follow, as well as the like compounds disclosed in US. Pat. No. 3,214,454 and 3,297,578, that a number of these can be described as methanol phosphonic acid derivatives having the following Formula D:

Formula D where R is independently selected from the group consisting of an alkyl group up to four carbon atoms and phosphonate groups, and R is selected from the group consisting of alkyl groups having up to 4 carbon atoms, when R, is a phosphonate group and where n is 0 to 6, when R is an alkyl group; and watersoluble salts thereof.

Specific methanol phosphonic acid compounds thus disclosed include, for example, l-hydroxy, ethylidene diphosphonic acid (i.e., ethanol, or methyl methanol, 1,1-diphosphonic acid); l-hydroxy. propylidene diphosphonic acid (i.e., ethyl methanol diphosphonic acid); l,o-dihydroxy-l,6-dimethyl, hexamethylene diphosphonic acid (i.e., tetramethylene bis (methyl methanol phosphonic acid)) and its sodium salt (Examples 44 and 1 l0): l,4-dihydroxy-1,4-diethyl. tetramethylene diphosphonic acid (i.e., dimethylene bis- (ethylmethanol phosphonic acid)): 1.3-dihydroxy-L3- dipropyl trimethylene diphosphonic acid (i.e., methylene bis (propylmethanol phosphonic acid)) and its sodium salt (Examples 46 and 112); dihydroxy, diethyl, ethylene diphosphonic acid (i.e., bis(ethylemethanol phosphonic acid)) and its sodium salt (Examples 52 and l 18); and l-hydroxy butylidene diphosphonic acid (i.e., propyl methanol diphosphonic acid).

The compositions of this invention also contain from 1 to and preferably from 25 to 45 percent of an azole compound and/or from 1 to and preferably from 25 ti 45 percent of a water-soluble zinc salt. Preferably, both the azole compound and zinc salts are used in the composition of this invention is the stated concentrations. It will be seen that the use of the more common water-soluble zinc salts such as zinc nitrate (Zn(NO molecular weight 189) zinc chloride (ZnCl molecular weight 136.29) and zinc sulfate (ZnSO or ZnSO -H O, molecular weight 161.44 and 179.44, respectively) in the aforesaid concentrations will provide zinc ion (Zn) concentrations from as little as 0.345 weight percent (as 1 percent Zn(NO to as high as 45.5 weight percent (equivalent to 95 percent ZnCl Thus the weight ratio of zinc (in the form of one of said water-soluble salts) to phosphonic acid compound may range from about 0.345280 to about 45.521 or, in other words, from about 1:232 to about 120.022. At the preferred concentrations of zinc salt the weight ratio of zinc ion may range from about 8.64:80 (Zn equivalent in 25 weight percent of Zn(NO to about 21.511 (Zn equivalent in 45 weight percent of ZnCl or in other words, from about 1:9.27 to about [10.0465. As seen in the following specific Examples 5 and 7, a typical zinc to phosphonic acid compound weight ratio is 1:1.

Azoles are nitrogen containing heterocyclic 5- membered ring compounds, and azoles which are suit able in the composition of this invention include triazoles, pyrazoles, imidazoles, isoxazoles, oxazoles, isothiazoles, thiazoles and mixtures thereof as disclosed in US. Pats. No. 2,618,608, No. 2,742,369, and No. 2,941,953.

The triazoles which can be employed in the composition of this invention are any water-soluble 1,2,3- triazoles such as 1,2,3-triazole itself or a substituted 1,2,3-triazole where the substitution takes place in either the 4 or 5 position (or both) of the triazole ring as shown here by the structural formula:

5 2N loll Suitable triazoles include benzotriazole (the preferred triazole); 4-phenyl-1.2,3-triazole; 1,2-napthotriazole; and 4-nitrobenzotriazole; and the like.

The pyrazoles which can be used in the composition of this invention include any water-soluble pyrazoles such as pyrazole itself or a substituted pyrazole where the substitution takes place in the 3, 4, or 5 position (or several of these positions) of the pyrazole ring as shown by the structural formula:

Suitable pyrazoles include pyrazole: 3,5-dimethyl pyrazole: 6-nitroindazole: 4-benzyl pyrazole; 4,5-dimethyl pyrazole; and 3-allyl pyrazole; and the like.

The imidazoles which can be used in the composition of this invention include any water-soluble imidazoles such as imidazole itself or a substituted imidazole position of this invention include imidazole; adenine; quanine; benzimidazole; S-methyl benzimidazole; 2-

phenyl imidazole; 2-benzyl imidazole; 4-allyl imidazole; 4-(betahydroxy ethyl)-imidazole; purine; 4-methyl imidazole; xanthine; hypoxanthene; 2-

methyl imidazole; and the like.

lsoxazoles which can be employed in the composition of this invention include any water-soluble isoxazole such as isoxazole itself or a substituted isoxazole where the substitution takes place in the 3, 4 or 5 position (or several of these positions) of the isoxazole ring as shown here by the structural formula:

1 HG 2N Hl J H Suitable isoxazoles include isoxazole; 3- mercaptoisoxazole; 3-mercaptobenzisoxazole; benzisoxazole; and the like.

The oxazoles which can be employed in the composition of this invention include any water-soluble oxazoles such as oxazole itself or a substituted oxazole where the substitution takes place in the 2, 4 or 5 position (or several of these positions) of the oxazole ring as shown here by the structural formula:

HC5 1 H Suitable oxazoles include oxazole; 2-mercaptoxazole; Z-mercaptobenzoxazole; and the like.

The isothiazoles which can be employed in the process of this invention include any water-soluble isothiazoles such as isothiazole itself or a substituted isothiazole where the substitution takes place in either the 3, 4 or 5 position (or several of these positions) of the isothiazole ring as shown here by the structural formula:

H05 1 2N n u n Suitable isothiazoles include isothiazole. 3- mercaptoisothiazole: 3-mercaptobenzisothiazole: benzisothiazole; and the like.

The thiazoles which can be used in the composition of this invention include any water-soluble thiazole such as thiazole itself or a substituted thiazole where the substitution takes place in the 2, 4 or 5 position (or several of these positions) of the thiazole ring as shown here by the structural formula:

suitable thiazoles include thiazole: 2- mercapthothiazole; Z-mercaptobenzothiazole; benzothiazole; and the like.

In the above azole compounds, the constituents substituted in the azole rings can be alkyl, aryl, aralkyl, alkylol, and alkenyl radicals so long as the substituted azole is water-soluble.

The zinc salts which can be employed in the composition of this invention include water-soluble zinc salt such as zinc sulfate, zinc chloride, zinc nitrate, alkali metal-zinc phosphate glasses, crystalline alkali metalzinc polyphosphates, and the like.

Aqueous systems can be treated with aqueous solutions containing from 1 to percent and preferably from 1 to 10 percent of the compositions of this invention. These solutions can be made by premixing the ingredients of this composition and then adding the mixture to water, or by adding the individual ingredients of the composition of this invention separately to water. These aqueous feed solutions are stable and can be stored prior to use.

In the methods of this invention for preventing corrosion of metals in contact with aqueous liquids, from 1 to 10,000 ppm. and preferably from 1 to 100 of the organophosphonic acid compounds, and from 1 to l0,000 ppm. and preferably from 1 to 100 ppm. of the azole compounds and/or from 1 to 10,000 and preferably from 2 to 200 ppm. of the water-soluble zinc salts are maintained in aqueous liquid. Preferably, both the azoles and zinc salts are maintained in the systems in the stated concentrations.

The aqueous corrosion resistant solutions of this invention are solutions of at least 1 and preferablyfrom 5 to 200 ppm. of the compositions of this invention. The ingredients can be added to the aqueous solutions either in premixed solid or solution or individual solids or solutions to form this aqueous solution composition.

The compositions of this invention are non-toxic and prevent corrosion of metals in contact with aqueous liquids. These compositions can be substituted for chromate base corrosion inhibitors previously used where the toxicity of the chromate makes its use undesirable or where disposal of corrosion inhibiting solutions containing chromates raises serious water pollution problems requiring extensive pretreatment to remove the chromates prior to disposal of such solutions. The compositions of this invention in aqueous solutions prevent corrosion of metal parts such as heat exchangers, engine jackets, and pipes and particularly prevent metal loss, pitting, and tuberculation of iron base alloys, copper alloys, and aluminum alloys in contact with water.

This invention is further illustrated by the following specific but non-limiting examples.

EXAMPLE 1 Calcium sulfate dihydrate 445 ppm. Magnesium sulfate heptahydrate 519 ppm. Sodium bicarbonate I ppm. Calcium chloride 136 ppm.

During the test, the circulating water was fed to a closed circulating test system at a rate of 5 gallons per day, the overflow from the test system being discharged to waste.

In the closed circulating system, circulating water having a temperature of 130 F. and pH of 6.5-7.0 was fed at a rate of 1 gallon per minute to a coupon chamber containing test coupons for the corrosion test. Water from the coupon chamber was then passed through an arsenical admirality brass tube surrounded by a jacket through which a heating fluid having an initial temperature of 240 F. was countercurrently passed. The circulating water was then cooled to 130 F. and recirculated through the system. The total circulating time for each test was 10 days.

Mild steel, brass (33 wt. percent zinc), copper and aluminum coupons having an average area of 26.2 cm. were used in the test chamber. The coupons were carefully cleaned and weighed before use. Following the test, each coupon was cleaned with inhibited hydrochloric acid, rinsed, dried and weighed to deterine the corrosion rate in mils per year. A comparison of the corrosion rates of the individual ingredients of the composition of this invention with combinations of these ingredients according to this invention were found to be as shown in Table A.

TABLE A E Corrosion rate in mils per year ample Alumi- Cop- No. Additive Steel num per Brass Blank (no treatment) 15.0 11. 2.0 3. 0 Zn++, 10 p.p.rn 15.3 8.2 1.6 1.4 llenzotriazole, 10 p.p.m. 24. 5 5.8 0.3 O. 2 llydroxy ethylidene diphos- 11. 1 7. 7 0.7 2. 2

phonic acid, p.p.m. .3 Zn, 10 p.p.m., hydroxy 8.4 5.4 2.2 2.0

cthylideno diphosphoniu acid, 10 p.p.m. 6 Benzotrlazole, 10 p.p.m., 5.7 4.0 0.2 0.2

hydroxy cthylidene diphosphonic acid, 10p.p.m. T Zn++, 10 p.p.m., benxotria 2.0 0.2 0.2 0.3

sole. l0 p.p.m., hydroxy ethylidene diphosphonic acid, 10 p.p.m.

As shown in Table A, Examples 5, 6 and 7 corresponding to the compositions of this invention provide a corrosion protection far greater than would be expected in view of the effects of the individual components thereof.

EXAMPLE 8 The corrosion rates in mils per year of aluminum in contact with liquid containing 10 ppm. Zn and 10 ppm. of benzotriazole according to the above test procedure was found to be 1.1.

Examples of other compositions according to this invention are shown in Table B.

Example No.

TABLE B Ingredients wt.%

Zinc sulfate 70.0%; benzotriazole 30.0%

Zinc chloride 40.0%; hydroxy ethylidene diphosphonic acid 60.0%

Benzotriazolc 35.5%; hydroxy ethylidene diphosphonic acid 64.5%

Zinc nitrate 70.0%; benzotriazolc 15.0%; hydroxy ethylidene diphosphonic acid 15.0%

Sodium trimethylenediphosphonate 15%;

pyrazole 15%; zinc sulfate monohydrate Decamethylenediphosphonic acid 15%;

3,5dimethy1 pyrazole 15%; zinc sulfate monohydrate 70% Sodium l,G-dihydroxyJ,6-dimethyl,

hexamethy lenediphosphonate 15%; imidazole 15%; zinc sulfate monohydrate 70% 1 -amino-2-phenylethane-1 1 -diphosphonic acid 15%;2benzy1imidazo1e 15%; zinc sulfate monohydrate 70% Sodium 1,3-dihydroxy,l,S-dipropyl,

trimethylenediphosphonate 15%; isoxazole 15%; zinc sulfate monohydrate 70% Zinc l-aminoethaneJ,l diphosphonate 15%; benzisoxazole 15%; zinc sulfate monohydrate 70% l-aminoethane-l,l-diphosphonic acid monoethyl ester 15%; Z-mercaptobenzoxazole 15%; zinc sulfate monohydrate 70% Tin methylenediphosphonate 15%;

isothiazole 15%; zinc sulfate monohydrate 70% Butylidenediphosphonic acid 15%;

1,2-naphthotriazole 15%; zinc sulfate monohydrate 70% l-aminobenzyl-l ,1 'diphosphonic acid 15%; 4 nitrobenzotriazole 15%; zinc sulfate monohydrate 70% Sodium dihydroxy, diethyl,

ethylenediphosphonate 15%; benzotriazole 15%; zinc sulfate monohydrate 70% Magnesium methylencdiphosphonate 50%;

1,2,3-triazole 50% Zinc isopropylidenediphosphonate 50%;

benzotriazole 50% Sodium trimethylenediphosphonate 50%;

pyrazole 50% Decamethylenediphosphonic acid 50%;

3,5-dimethyl pyrazole 50% Sodium 1,6-dihydroxy, 1,6-dimethyl,

hexamethylenediphosphonate 50 imidazole 50% l-amino-Z-phenylethanel ,1 -diphosphonic acid 50%; 2 benzyl imidazole 50% Sodium 1,3-dihydroxy, 1,3-dipropyl,

trimethylenediphosphonate 50%; isoxazole 50% Zinc l-aminoethane-l,l-diphosphonate 50%; benzisoxazole 50% l-aminoethane-1,l'diphosphonic acid monoethyl ester 50%; Z-mercaptobenzoxazole 50% Tin methylenediphosphonate 50%;

isothiazole 50% Butylidenediphosphonic acid 50%;

1,2-naphthotriazole 50% l-aminobenzyl-l ,l-diphosphonic acid 50%; 4-nitrobenzotriazole 50% Sodium dihydroxy, diethyl,

ethylenediphosphonate 50%; benzotriazole 50% Magnesium methylenediphosphonate 30%;

zinc sulfate monohydrate 70% Zinc isopropylidenediphosphonate 30%;

zinc sulfate monohydrate 70% Sodium trimethylenediphosphonate 30%;

zinc sulfate monohydrate 70% Decamethylenediphosphonic acid 30%;

zinc sulfate monohydrate 70% Sodium 1,6-dihydroxy, 1,6-dimethyl,

hexamethylenediphosphonate 30%; zine sulfate monohydrate 70% 1 -amino-2-phenylethane-l ,l -diphosphonic acid 30%; zinc sulfate monohydrate 70% Sodium 1,3-dihydroxy, 1,3-dipropyl,

trimethylene-diphosphonate 30%; zinc sulfate monohydrate 70% Zinc l-aminoethane-l,l-diphosphonate 30%; zinc sulfate monohydrate 70% l-aminoethane-l ,l -diphosphonic acid monoethyl ester 30%; zinc sulfate monohydrate 70% Tin methylenediphosphonate 30%; Zinc sulfate monohydrate 70% Butylidenephosphonic acid 30%; zinc sulfate monohydrate 70% l-aminobenzyl-l,l-diphosphonic acid 30%; zinc sulfate monohydrate 70% Sodium dihydroxy. diethyl,

ethylenediphosphonate 30%; zinc sulfate monohydrate 70% l-hydroxy ethylidene diphosphonic acid 40%; zinc chloride 30%; benzotriazole 30% l-hydroxy propylidene diphosphonic acid 30%; zinc sulfate monohydrate 50%; benzotriazole l-hydroxy ethylidene diphosphonic acid zinc nitrate 55%; mercaptobenzothiazole 20% l-hydroxy butylidene diphosphonic acid 20%; zinc sulfate monohydrate 50%; mercaptobenzothiazole What is claimed is:

l. A composition useful for inhibiting corrosion in aqueous systems, said composition consisting essentially of one part by weight zinc in the form of a watersoluble zinc salt; from 0.02 to about 300 parts by weight of a water-soluble organic phosphonate compound having the formula where R is independently selected from the group consisting of alkyl groups up to four carbon atoms, and

phosphonate groups, and R is selected from the group consisting of alkyl groups having up to four carbon atoms, when R, is a phosphonatc group; and

where n is 0 to 6, when R is an alkyl group, and watersoluble salts and "esters thereof; and corrosion inhibiting amounts of a copper corrosion inhibitor selected from the group consisting of 1,2,3-triazoles, thiazoles, oxazoles, imidazoles, isoxazoles, isothiazoles and pyrazoles.

2. The composition of claim 1 in which the watersoluble zinc salt is zinc sulfate. 

2. The composition of claim 1 in which the water-soluble zinc salt is zinc sulfate.
 3. The composition of claim 1 in which the phosphonate compound is ethanol 1,1-diphosphonic acid or water-soluble salt thereof.
 4. A method of inhibiting corrosion in aqueous systems comprising maintaining therein an amount of the composition of claim 1 to provide up to about 100 ppm. copper corrosion inhibitor. 